Everything You Need to Know about Narcissists, Psychopaths, and Abuse - click on this link: http://www.narcissistic-abuse.com/faq1.html
The narcissist may study a given subject diligently and in great depth in order to impress people later with this newly acquired erudition. But, having served its purpose, the narcissist lets the knowledge thus acquired evaporate. The narcissist maintains a sort of a "short-term" cell or warehouse where he stores whatever may come handy in the pursuit of Narcissistic Supply. But he is almost never really interested in what he does, studies, and experiences.
From the outside, this might be perceived as instability. But think about it this way: the narcissist is constantly preparing for life's "exams" and feels that he is on a permanent trial. It is common to forget material studied only in preparation for an exam or for a court appearance.
Short-term memory is perfectly normal. What sets the narcissist apart is the fact that, with him, this short-termism is a CONSTANT state of affairs and affects ALL his functions, not only those directly related to learning, or to emotions, or to experience, or to any single dimension of his life.
Thus, the narcissist learns, remembers and forgets not in line with his real interests or hobbies, he loves and hates not the real subjects of his emotions but one dimensional, utilitarian, cartoons constructed by him. He judges, praises and condemns â all from the narrowest possible point of view: the potential to extract Narcissistic Supply.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/thebook.html)